Dialkyl dicarbonates, also known as dialkyl pyrocarbonates, are useful as fermentation inhibitors in wines and fruit juices, as well as reagents in chemical synthesis. Several methods are known for preparing dialkyl dicarbonates, but these methods suffer from various disadvantages such as hazardous starting materials (e.g., phosgene), low yields, and time consuming and/or cumbersome purification steps.
In FR 1,483,460 (Shamshurin--Institut Khimii an Moldavskoisar, granted in 1967) alkyl chloroformate is reacted with potassium or sodium carbonate in the presence of a tertiary amine as a catalyst. While this method is in many respects an improvement over the prior art which proceeded it, it nonetheless is less than an ideal solution. In particular, the purification step necessary to separate the dialkyl dicarbonate from the tertiary amine is rather cumbersome, and the overall process has a disappointingly low yield.
U.S. Pat. No. 4,929,748 discloses a method of preparing dialkyl dicarbonate which comprises contacting an alkyl haloformate with an alkali metal carbonate in the presence of a catalytic amount of a crown ether and a solvating amount of a solvent.
French Publication No. 2,220,564 discloses a method of preparing dialkyl dicarbonate by carbonation of the corresponding alkali metal alcoholate in tetrahydrofuran followed by reaction with an excess of chloroformate. This method has the disadvantages of having to deal with large amounts of solvent and various hazardous and expensive materials such as metal alkoxides.
An article distributed at the "Chemicals and the Environment Symposium", held at the Fall 1992 Chemspec Meeting, (New Brunswick, N.J.), describes a process for the preparation of dialkyl and diaryl pyrocarbonates. The process generally comprises reacting a chloroformate with 50% sodium hydroxide in the presence of a catalyst without added solvent.
U.S. Pat. No. 5,151,542 discloses a process for the preparation of di-tertiary butyl dicarbonate which comprises reacting alkali metal tertiary butyl carbonate with methanesulfonyl chloride.
Prior art methods for preparing dialkyl dicarbonates suffer various drawbacks including problems arising from the use of toxic complexing agents or cosolvents, corrosion problems, unsatisfactory space-time yields, and problems incurred in working up the reacting mixture.
Accordingly, it is an object of the present invention to provide a process for preparing dialkyl dicarbonates which overcomes the disadvantages of the prior art and is safe, economical and provides high yields of the desired product.